1. Field of the Invention
The present invention relates to a method and an apparatus for processing a ceramic green sheet, which is used for manufacturing a multilayer ceramic electronic component, by laser beam irradiation.
2. Description of the Related Art
A multilayer chip inductor, which is known as a kind of multilayer ceramic electronic component, is manufactured as described below.
First, a ceramic green sheet of a size such that many chips can be obtained is prepared, and a matrix of through holes are formed at predetermined intervals in this ceramic green sheet. These through holes are formed in the following way. While an X-Y table on which the ceramic green sheet is held is moved in the X direction at a predetermined speed, a laser beam is applied intermittently to the ceramic green sheet to form a row of through holes. Subsequently, the table is stopped once, and row change is made by moving the table in the Y direction through a predetermined distance. Then, while the table is moved in the X direction at a predetermined speed, a laser beam is again applied intermittently to the ceramic green sheet. This operation is repeated until all the through holes are formed.
Next, screen printing of coil conductor paste is performed in a predetermined pattern on one surface of the ceramic green sheet in which the matrix of through holes is formed. The patterns of conductor paste are formed in number corresponding to the number of chips to be obtained, and some of paste patterns are charged in the through holes simultaneously with the printing.
Next, the ceramic green sheets on which paste patterns corresponding to the number of chips to be obtained are formed and ceramic green sheets having neither through holes nor paste patterns are stacked in a predetermined order and are pressed. By this stacking and pressing operation, the paste patterns between the sheets are connected in a coil form via the charged paste in the through holes.
Next, the multilayer sheet laminate is cut to a unit dimension corresponding to the dimension of the component, and the multilayer chips obtained by the cutting are fired. Finally, electrode paste is applied and baked onto the external surface of the fired chip to form an external electrode. As necessary, solder film or the like is formed on this surface.
In the conventional processing method, the matrix of through holes is formed in a ceramic green sheet as described above. That is to say, while a table is moved in the X direction at a predetermined speed, a laser beam is applied intermittently to the ceramic green sheet to form a row of through holes. Subsequently, the table is stopped once, and row change is made by moving the table in the Y direction through a predetermined distance. Then, while the table is moved in the X direction at a predetermined speed, a laser beam is again applied intermittently to the ceramic green sheet. This operation is repeated until all the through holes are formed.
However, in such a processing method, when the table is moved in the X direction to form a row of through holes, an acceleration region needed for the table to reach the predetermined speed and a deceleration region needed for the table to stop must be provided. Also, time for moving the table in the Y direction, which has been stopped after the row of through holes were formed, and for stopping the table again is necessary each time the row change is made.
That is to say, at the time of processing, the table must be moved needlessly in the X direction through a distance corresponding to the aforementioned acceleration region and deceleration region. Also, since the time for row change is necessary in proportion to the number of row changes. Therefore considerably much time is needed to form the desired matrix of through holes in one ceramic green sheet even if the table movement speed in the X and Y directions is increased.
An object of the present invention is to provide a new processing method in which processing for forming a matrix etc. of through holes or concave portions in a ceramic green sheet by laser beam irradiation can be performed at a high speed, and to provide a processing apparatus suitable for carrying out this processing method.
To attain the above object, a first processing method in accordance with the present invention comprises the steps of: rotating a cylindrical drum in which a ceramic green sheet is removably attached on an outer peripheral surface thereof with the drum centerline being the axis; processing the ceramic green sheet along one circular path by irradiating a laser beam toward the outer peripheral surface of the rotating drum; and changing the processing path by moving at least one of the rotating drum and a beam irradiated position through a predetermined distance in the direction of drum centerline each time the processing on one circular path is completed.
According to this processing method, the processing along the circular path can be performed repeatedly on the ceramic green sheet attached on the outer peripheral surface of the rotating drum while the position is changed in the direction of drum centerline. If the laser beam is applied intermittently to the ceramic green sheet, a matrix of through holes or concave portions can be formed easily on the ceramic green sheet. Also, if the laser beam is applied continuously to the ceramic green sheet, the ceramic green sheet can be cut to a zonation shape, or parallel concave portions can be formed in the ceramic green sheet. Since the processing on the ceramic green sheet can be performed without the stoppage of rotation of the drum, the processing time can be shortened significantly and the work efficiency can be increased as compared with the conventional processing method.
Also, a second processing method in accordance with the present invention comprises the steps of: rotating a cylindrical drum in which a ceramic green sheet is removably attached on an outer peripheral surface thereof with the drum centerline being the axis; and processing the ceramic green sheet along a spiral path by irradiating a laser beam toward the outer peripheral surface of a rotating drum while at least one of the rotating drum and a beam irradiated position is moved in the direction of drum centerline.
According to this processing method, the processing along the spiral path can be performed on the ceramic green sheet attached on the outer peripheral surface of the rotating drum. If the laser beam is applied intermittently to the ceramic green sheet, a matrix of through holes or concave portions can be formed easily on the ceramic green sheet. Also, if the laser beam is applied continuously to the ceramic green sheet, the ceramic green sheet can be cut to a spiral shape, or spiral concave portions can be formed in the ceramic green sheet. Since the processing on the ceramic green sheet can be performed without the stoppage of rotation of the drum, the processing time can be shortened significantly and the work efficiency can be increased as compared with the conventional processing method.
On the other hand, a first processing apparatus in accordance with the present invention comprises: a cylindrical drum capable of attaching the ceramic green sheet removably on an outer peripheral surface thereof; first driving means for rotating the drum with the drum centerline being the axis; beam irradiating means for irradiating a laser beam toward the outer peripheral surface of the rotating drum; second driving means for changing a processing path by moving at least one of the rotating drum and a beam irradiated position in the direction of drum centerline; first control means for controlling the first driving means and the beam irradiating means so that the ceramic green sheet is processed along one circular path; and second control means for controlling the second driving means so that at least one of the rotating drum and the beam irradiated position is moved through a predetermined distance in the direction of drum centerline each time the processing on one circular path is completed.
According to this first processing apparatus, the above-described first processing method can be carried out properly and stably.
Also, a second processing apparatus in accordance with the present invention comprises: a cylindrical drum capable of attaching the ceramic green sheet removably on an outer peripheral surface thereof; first driving means for rotating the drum with the drum centerline being the axis; beam irradiating means for irradiating a laser beam toward the outer peripheral surface of the rotating drum; second driving means for obtaining a spiral path by moving at least one of the rotating drum and a beam irradiated position in the direction of drum centerline; and control means for controlling the first driving means, beam irradiating means, and second driving means so that the ceramic green sheet is processed along the spiral path.
According to this second processing apparatus, the above-described second processing method can be carried out properly and stably.